Numerous types of communication links and communication protocols are used to interconnect devices and allow interconnected devices to communicate with one another. This has become true with connections between a computer and its peripheral devices such as printers, scanners, backup tape drives, modems, keyboards, mouse, and others.
First to appear was the RS-232 serial communication. The RS-232 serial communication protocol provided adequate communication speeds for relatively slow devices. However, as some devices, such as printers, gained speed, the RS-232 protocol did not provide a reliable link between the computer and the device. A parallel protocol commonly known as centronics was created. The centronics protocol provided adequate communications from the computer to the device, but communication from the device to the computer was very limited. Eventually, the centronics port could not provide the high-speed communication link required. To allow bidirectional communications and higher speed, the IEEE-1284-1994 (IEEE Standard Signaling Method for Bidirectional Parallel Peripheral interface for Personal Computers, herein incorporated by reference) communication protocol was developed. At the first layer, or physical layer, the 1284 protocol uses bi-directional data lines; all lines use controlled impedance to allow for higher speed. The 1284 protocol is backwards compatible with the centronics protocol.
Recently, there has been developed yet another protocol for interfacing peripheral devices to the computer known as the Universal Serial Bus (USB) as described in USB Specification Revision 1.0 herein incorporated by reference. At the first layer, physical layer, the USB uses serial data with controlled impedance to achieve a 12 Megabits per second data channel. The USB is not backward compatible with any of the previously mention protocols.
Many of the peripheral devices that communicate to the computer are increasing in speed and decreasing in cost and size. For example, as printers have progressed from 300 dpi to 600 dpi to 1200 dpi, the amount of data has increased 16 fold. Similarly, these same printers have increased from 4 pages per minute to 24 pages per minute. The price and size has remained relatively constant.
To help increase the likelihood that the peripheral device will operate with the large number and widely varying computers, the peripheral device must support several communication protocols. However, at present, this would require several different connectors; RS-232, centronics/1284, and USB for example. This adds additional cost and uses precious printed circuit assembly (PCA) space. Many printers have already added a network option.
Prior to the present invention, there are two ways to support both the centronics/1284 and USB ports. First, as described above, the peripheral designer can design the product with both connectors. Second, the designer may elect to support one on the peripheral and then provide or sell an external active converter.